Switching power supply output overvoltage protection circuit and switching power supply system

Abstract

The utility model discloses a switching power output overvoltage protection circuit and switching power system, and the protection system circuit includes the following function subcircuit: output voltage sampling circuit, reference voltage circuit, comparator with open circuit collector output end, isolation circuit and level conversion circuit. The circuit still includes hysteresis positive feedback network. The network passes through second reference voltage dividing resistor (with diode series branch) and electrically connects the open circuit collector output end of comparator to its noninverting input end, and the noninverting input end of comparator still connects to reference voltage circuit through first reference voltage dividing resistor. The open circuit collector output end of comparator is also used for driving isolation circuit. The topology structure of the utility model utilizes the output state of comparator to change its reference threshold dynamically, generates overvoltage protection threshold and lower overvoltage recovery threshold, and the hysteresis voltage formed can prevent the oscillation near the threshold point, improves the anti -interference ability, security and stability of circuit.

Description

Technical Field

[0001] This utility model relates to the field of switching power supplies, and in particular to a switching power supply output overvoltage protection circuit and switching power supply system. Background Technology

[0002] Switching power supplies (SMPS), as core components of modern electronic devices, have permeated various fields such as communications, industrial control, consumer electronics, and data centers. The stability and reliability of SMPS directly affect the safe operation of the entire system. Among the various protection functions of a SMPS, output overvoltage protection (OVP) is used to protect downstream loads (such as expensive processors, FPGAs, or precision sensors) from damage. If the OVP circuit fails or responds abnormally, the instantaneous uncontrolled surge in output voltage can cause irreversible and permanent physical damage to the load. Therefore, designing a highly reliable and interference-resistant output overvoltage protection circuit can ensure the safety of electronic systems.

[0003] Currently, existing technologies for secondary-side output overvoltage protection in switching power supplies include using a voltage comparator for threshold detection. In this approach, the circuit system uses a precision voltage comparator (such as an LM393) or an operational amplifier. This circuit samples the output voltage of the switching power supply in real time using a resistor divider network and compares this sampled voltage with a fixed reference voltage provided by a precision reference source (such as a TL431 or a Zener diode). When the sampled voltage exceeds a single, fixed reference threshold, the comparator determines that an overvoltage has occurred, its output state flips, and a fault signal is generated. This fault signal is then transmitted from the secondary side to the primary side through isolation devices such as optocouplers to shut down or suppress the drive output of the PWM control chip, cutting off energy transfer and causing the output voltage to drop, thus achieving overvoltage protection.

[0004] However, the aforementioned existing technologies rely on single-threshold comparators, which suffer from system instability near the protection threshold in complex real-world application environments. Therefore, further research and innovation are needed to address these issues in the existing technologies. Utility Model Content

[0005] Purpose of the utility model: In view of the above problems of the prior art, this application provides a switching power supply output overvoltage protection circuit and a switching power supply system.

[0006] Technical solution: Firstly, a switching power supply output overvoltage protection circuit is provided, comprising:

[0007] Output voltage sampling circuit;

[0008] Reference voltage circuit;

[0009] Isolation circuit;

[0010] A comparator has a non-inverting input, an inverting input, and an open-collector output.

[0011] First reference voltage divider resistor;

[0012] The output of the output voltage sampling circuit is electrically connected to the inverting input of the comparator; the output of the reference voltage circuit is electrically connected to the non-inverting input of the comparator; one end of the first reference voltage divider resistor is electrically connected to the non-inverting input of the comparator, and the other end is connected to the output of the reference voltage circuit.

[0013] In conjunction with the first aspect, in some implementations of the first aspect, the non-inverting input of the comparator is also electrically connected to its open-collector output via a branch consisting of a second reference resistor and a diode connected in series.

[0014] In conjunction with the first aspect, in some implementations of the first aspect, the isolation circuit is an optocoupler; the optocoupler includes a light-emitting diode and a phototransistor, with the input terminal of the light-emitting diode electrically connected to the open collector output terminal of the comparator.

[0015] In conjunction with the first aspect, in some implementations of the first aspect, the switching power supply output overvoltage protection circuit further includes a primary-side PWM control chip, which has a feedback FB pin; the output terminal of the optocoupler's phototransistor is electrically connected to the primary-side level conversion circuit.

[0016] It is connected to the level conversion circuit, and the output of the level conversion circuit is electrically connected to the feedback pin of the primary-side PWM control chip.

[0017] In conjunction with the first aspect, in some implementations of the first aspect, the output voltage sampling circuit includes a resistor divider consisting of a first resistor and a second resistor connected in series; the connection point of the first resistor and the second resistor constitutes the output terminal of the output voltage sampling circuit, which is electrically connected to the inverting input terminal of the comparator.

[0018] In conjunction with the first aspect, in some implementations of the first aspect, the reference voltage circuit includes a third resistor and a parallel voltage reference source; the third resistor is electrically connected between the output voltage rail and the non-inverting input of the comparator; the parallel voltage reference source is electrically connected between the non-inverting input of the comparator and ground.

[0019] In conjunction with the first aspect, in some implementations of the first aspect, the overvoltage protection circuit for the switching power supply output also includes a current-limiting resistor; the current-limiting resistor is connected in series electrically between the open collector output terminal of the comparator and the light-emitting diode of the optocoupler.

[0020] Secondly, a switching power supply system is provided, comprising:

[0021] Primary-side PWM circuit;

[0022] transformer;

[0023] Secondary rectifier circuit;

[0024] The switching power supply output overvoltage protection circuit as described in the first aspect.

[0025] In conjunction with the second aspect, in some implementations of the second aspect, the switching power supply system is a flyback switching power supply system.

[0026] Beneficial effects: This invention solves the technical problem that existing single-limit comparators are susceptible to noise interference near the overvoltage protection point, resulting in oscillation and instability. The related technical effects will be described in detail below with reference to specific embodiments. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of a partial structure of a switching power supply output overvoltage protection circuit provided in an embodiment of this application.

[0028] Figure 2 This is a partial structural diagram of a switching power supply system provided in an embodiment of this application.

[0029] Figure 3 This is a schematic diagram of the secondary rectifier circuit provided in an embodiment of this application.

[0030] Figure 4 This is a schematic diagram of another switching power supply output overvoltage protection circuit provided in an embodiment of this application.

[0031] Figure 5 This is a schematic diagram of a primary-side PWM circuit structure provided in an embodiment of this application.

[0032] Figure 6 This is a schematic diagram of a primary-side level conversion circuit provided in an embodiment of this application. Detailed Implementation

[0033] To enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the protection scope of the present invention.

[0034] It should be noted that the terms "first," "second," etc., used in this specification are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the present invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "including" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that includes a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0035] To address the aforementioned issues, the applicant conducted in-depth searches and analyses, and discovered:

[0036] Single-threshold comparators are extremely sensitive to noise and lack the necessary anti-interference capabilities. Switching power supplies themselves are strong sources of electromagnetic interference, and their output voltage is superimposed with high-frequency switching ripple and various coupling noises. When the output voltage fluctuates around the overvoltage protection threshold due to load transients, the ripple and noise will cause the sampled voltage to repeatedly cross this single threshold. This will cause high-frequency jitter or oscillation at the comparator's output. This unstable fault signal, transmitted to the primary side, will cause the PWM controller to repeatedly start and stop, not only failing to achieve stable protection but also impacting the system, and in severe cases, even causing the control chip to fail.

[0037] Furthermore, the single-threshold design also introduces inherent problems in the recovery mechanism. Once protection is triggered, the output voltage has just begun to drop. If the sampled voltage falls below the threshold, the protection state will be immediately lifted, and the PWM controller will attempt to restart. However, restarting may cause the voltage to touch the threshold again, causing the system to fall into an unstable state of hiccups or low-frequency oscillations near the protection point, making it impossible to achieve both protection and controllable recovery.

[0038] To solve these problems, combined with Figures 1 to 5 The present invention will be specifically described through the following embodiments.

[0039] Example 1: This example provides a switching power supply system.

[0040] In this invention, the switching power supply system is a flyback switching power supply system. This system includes a primary-side PWM circuit, a transformer (T800), a secondary rectifier circuit, and an output overvoltage protection circuit for the switching power supply. The primary-side PWM circuit includes a primary-side PWM control chip (D802) and a switching transistor (Q800). The secondary rectifier circuit includes a rectifier diode (V806) and an output filter circuit (e.g., C811, C812) for generating the output voltage (VO) of the switching power supply.

[0041] The switching power supply output overvoltage protection circuit of this embodiment is used to overcome the problem that the single-limit comparator has poor anti-interference capability and is prone to oscillation near the protection point. The switching power supply output overvoltage protection circuit includes, in structure, an output voltage sampling circuit, a reference voltage circuit, a comparator (U3), an isolation circuit (U1), and a first reference voltage divider resistor (R4).

[0042] Specifically, the output voltage sampling circuit includes a resistor divider consisting of a first resistor (R1) and a second resistor (R2) connected in series, used to sample the output voltage (VO) of the switching power supply.

[0043] Furthermore, the reference voltage circuit includes a third resistor (R829) and a parallel voltage reference source (D806) (e.g., a 2.5V TL431 reference source) that powers it, providing a stable reference voltage for the comparator (U3).

[0044] Based on this, the comparator (U3) has a non-inverting input (+), an inverting input (-), and an open collector (OC) output.

[0045] Accordingly, the isolation circuit (U1) can be an optocoupler to achieve electrical isolation between the secondary protection signal and the primary.

[0046] The electrical connections of the circuit components described above are as follows:

[0047] The output terminal of the output voltage sampling circuit, i.e. the connection point of the first resistor (R1) and the second resistor (R2), is electrically connected to the inverting input terminal of the comparator (U3).

[0048] The output of the reference voltage circuit, i.e. the cathode of the parallel voltage reference source (D806), is electrically connected to the non-inverting input of the comparator (U3) through the first reference voltage divider resistor (R4).

[0049] In other words, the output of the reference voltage circuit and the series branch of the first reference voltage divider resistor are electrically connected to the non-inverting input of the comparator, and also to the series branch of the diode and the second reference voltage divider resistor; the open collector output of the comparator is also electrically connected to the input of the isolation circuit.

[0050] Optionally, the overvoltage protection circuit for the switching power supply output may also include a level shifting circuit; which is electrically connected to the output terminal of the phototransistor of the optocoupler.

[0051] Based on this, the open-collector output of comparator (U3) has two parallel signal paths, specifically including:

[0052] Firstly, the open collector output terminal is electrically connected to the non-inverting input terminal of the comparator (U3) through a diode (D1) and a second reference voltage divider resistor (R5), forming a positive feedback loop;

[0053] Secondly, the open collector output terminal is also electrically connected to the input terminal of the isolation circuit (U1) (i.e., the LED side of the optocoupler) to drive the protection action.

[0054] Through the circuit topology described above, this embodiment successfully constructs a hysteresis comparator circuit in the detection and response circuit. When the output voltage (VO) is normal, the comparator (U3) outputs a high level (OC is off, and the output voltage is determined by the pull-up voltage), and the power supply operates normally. When the output voltage (VO) rises and exceeds the first overvoltage protection threshold (UT) determined by the reference voltage... + When the comparator (U3) outputs a low level (i.e., OC is on, grounded), it drives the isolation circuit (U1) to shut down the primary-side PWM control chip (D802). Simultaneously, because U3 outputs a low level, the reference voltage at the non-inverting input of U3 decreases (from 2.5V to R5 / (R4+R5)*(2.5V-0.5V)). Therefore, when the output voltage (VO) drops, it must drop significantly below the first overvoltage protection threshold (UT). + The second overvoltage recovery threshold (UT) - When the overvoltage protection point is reached, the comparator (U3) can flip back to a high level, allowing the power supply to resume operation. This design has two different threshold voltages, forming a hysteresis voltage (ΔUT), which can prevent the output voltage from oscillating near the overvoltage protection point, improving the power supply's anti-interference capability, safety, and stability.

[0055] Example 2: Further explanation of the output voltage sampling circuit and the reference voltage circuit. The output voltage sampling circuit is used to achieve real-time sampling of the switching power supply output voltage (VO).

[0056] Specifically, the output voltage sampling circuit is structured as a resistor divider, consisting of a first resistor (R1) and a second resistor (R2) connected in series. The voltage division point of this resistor divider, i.e., the connection point between the first resistor (R1) and the second resistor (R2), is electrically connected to the inverting input (-) of the comparator (U3). After the output voltage (VO) is sampled by this resistor divider, the sampled signal is sent to the inverting input of the comparator.

[0057] Accordingly, the reference voltage circuit is used to provide a stable reference voltage for the comparator (U3). In one specific embodiment, the reference voltage circuit includes a third resistor (R829) and a parallel voltage reference source (D806). The connection is as follows: one end of the third resistor (R829) is electrically connected to the voltage rail (e.g., the output voltage VO), and the other end is connected to the cathode of D806, forming a current-limiting resistor. The intersection of the two is the output terminal of the reference circuit, and this section is connected to the non-inverting input terminal of U3 through R4.

[0058] Alternatively, the parallel voltage reference (D806) can be a TL431 adjustable precision reference source, which can provide a stable reference voltage of, for example, 2.5V to the non-inverting input (+) of the comparator (U3).

[0059] Example 3 describes the topology of the hysteresis comparator circuit, which is used to implement the anti-interference function of this invention. The comparator (U3) can be selected as having an open-collector (OC) output. The open-collector output of the comparator (U3) is electrically connected to its non-inverting input (+) via a branch formed by a diode (D1) and a second reference voltage divider resistor (R5) connected in series.

[0060] In this embodiment, the non-inverting input (+) of the comparator (U3) is also electrically connected to the output of the reference voltage circuit via the first reference resistor (R4).

[0061] The positive feedback network, consisting of the first reference voltage divider resistor (R4), the second reference voltage divider resistor (R5), and the diode (D1), defines two different operating thresholds for this circuit. Specifically, when the output voltage (VO) rises, causing the voltage sampled by R1 and R2 and sent to the inverting input (-) to exceed the reference voltage set by D806 (e.g., 2.5V), i.e., exceeding the overvoltage protection point ((R1 / R2+1)*2.5V), the open-collector output of comparator (U3) flips from high (OC off) to low (OC on). At this time, this low level causes the reference voltage at the non-inverting input of U3 to become R5 / (R4+R5)*(2.5V-0.5V), where 0.5V is the forward voltage drop of diode D1.

[0062] Therefore, when overvoltage protection is triggered and the output voltage (VO) begins to drop, this output voltage (VO) must drop to a new threshold much lower than the original overvoltage protection point, i.e., the overvoltage recovery point, in order for the voltage at the inverting input terminal (-) to be lower than the voltage of the new threshold (R5 / (R4+R5)*(2.5V-0.5V), causing the comparator (U3) output to flip back to a high level and the power supply to resume operation. The voltage threshold of this overvoltage recovery point is jointly determined by the reference voltage (2.5V) of R1, R2, R4, R5, and D806, as well as the forward voltage drop of the diode (D1). This recovery point voltage can be expressed as {R1 / R2+1)[R5 / (R5+R4)(2.5V-0.5V)]}. This design gives the circuit a clear hysteresis voltage, which can prevent the output voltage from oscillating near the overvoltage protection point due to noise and other factors, increasing the reliability of the power supply protection.

[0063] Example 4 provides a detailed description of the isolation circuit and control circuit. The isolation circuit is used to isolate the secondary-side protection signal from the primary-side control chip.

[0064] As an example, the isolation circuit (U1) is an optocoupler. The optocoupler (U1) includes an input terminal on the secondary side, namely a light-emitting diode, and an output terminal on the primary side, namely a phototransistor.

[0065] In one specific implementation, to provide a suitable drive current to the LED of the optocoupler (U1), the switching power supply output overvoltage protection circuit also includes a current-limiting resistor (R7). The current-limiting resistor (R7) is connected in series between the open-collector output of the comparator (U3) and the input of the LED of the optocoupler (U1). When the comparator (U3) outputs a high level (essentially an open-collector disconnect), current flows through the current-limiting resistor (R7) and the LED, turning on the LED of the optocoupler (U1).

[0066] On the primary side of the switching power supply, the phototransistor (output terminal) of the optocoupler (U1) is electrically connected to the primary-side level conversion circuit. The output of the level conversion circuit is electrically connected to the feedback pin (FB) of the PWM control chip (D802). When an overvoltage occurs in the secondary output voltage, the LED of the optocoupler (U1) on the secondary side does not conduct, and the phototransistor on the primary side also does not conduct. At this time, the level conversion circuit pulls the voltage of the feedback pin (FB) of the primary-side PWM control chip (D802) to a low level. This causes the primary-side PWM control chip (D802) to stop driving, and the power supply stops working. In this way, the overvoltage protection signal on the secondary side is isolated and transmitted to the primary side, realizing the shutdown of the switching power supply, preventing the output voltage of the protection power supply from continuing to rise and causing overvoltage in the downstream circuit, thus protecting the downstream circuit.

[0067] In summary, when the output voltage is near a single protection point, noise and ripple can cause the comparator output to oscillate, causing the PWM controller to repeatedly start and stop or hiccup.

[0068] This invention solves this problem by constructing a hysteresis comparator circuit. That is, by utilizing the open collector output of the comparator (U3), a positive feedback network consisting of a first reference voltage divider resistor (R4), a second reference voltage divider resistor (R5), and a diode (D1) is established to achieve one output with two functions.

[0069] When the output voltage exceeds the first overvoltage protection threshold (UT) + When the comparator (U3) outputs (OC disconnected), it simultaneously drives the optocoupler (U1) to turn off the PWM, and also immediately raises the reference voltage at the non-inverting input (+) of the comparator via (R4). Since the reference threshold has been dynamically raised, the output voltage (VO) is now at the original protection point (UT). + The noise or ripple in the vicinity can no longer cause the comparator to flip, thus eliminating the oscillation problem.

[0070] At the same time, only when the output voltage (VO) drops significantly below (UT) + The second overvoltage recovery threshold (UT) determined by (R4, R5, D1) is... - The comparator will only reset when (UT) is reached. + ) and (UT - The hysteresis voltage formed between the circuit and the circuit makes the circuit turn off decisively and the recovery delayed, avoiding the hiccup state and improving the anti-interference ability and stability of the protection circuit.

[0071] It should be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, this utility model will not describe the various possible combinations separately.

Claims

1. A switching power supply output overvoltage protection circuit, characterized in that, include: Output voltage sampling circuit; Reference voltage circuit; Isolation circuit; A comparator has a non-inverting input, an inverting input, and an open-collector output. First reference voltage divider resistor; The output of the output voltage sampling circuit is electrically connected to the inverting input of the comparator; the output of the reference voltage circuit is electrically connected to the non-inverting input of the comparator; one end of the first reference voltage divider resistor is electrically connected to the non-inverting input of the comparator, and the other end is connected to the output of the reference voltage circuit.

2. The switching power supply output overvoltage protection circuit according to claim 1, characterized in that, The non-inverting input of the comparator is also electrically connected to its open collector output via a branch consisting of a second reference resistor and a diode connected in series.

3. The switching power supply output overvoltage protection circuit according to claim 1, characterized in that, The isolation circuit is an optocoupler; the optocoupler includes a light-emitting diode and a phototransistor, and the input terminal of the light-emitting diode is electrically connected to the open collector output terminal of the comparator.

4. The switching power supply output overvoltage protection circuit according to claim 3, characterized in that, The switching power supply output overvoltage protection circuit also includes a primary-side PWM control chip, which has a feedback FB pin; the output terminal of the optocoupler's phototransistor is electrically connected to the primary-side level conversion circuit.

5. The switching power supply output overvoltage protection circuit according to claim 1, characterized in that, The output voltage sampling circuit includes a resistor divider consisting of a first resistor and a second resistor connected in series; the connection point of the first resistor and the second resistor constitutes the output terminal of the output voltage sampling circuit, which is electrically connected to the inverting input terminal of the comparator.

6. The switching power supply output overvoltage protection circuit according to claim 1, characterized in that, The reference voltage circuit includes a third resistor and a parallel voltage reference source; the third resistor is electrically connected between the output voltage rail and the non-inverting input of the comparator; the parallel voltage reference source is electrically connected between the non-inverting input of the comparator and ground.

7. The switching power supply output overvoltage protection circuit according to claim 3, characterized in that, The overvoltage protection circuit for the switching power supply also includes a current-limiting resistor; the current-limiting resistor is connected in series between the open collector output of the comparator and the light-emitting diode of the optocoupler.

8. A switching power supply system, characterized in that, include: Primary-side PWM circuit; transformer; Secondary rectifier circuit; The switching power supply output overvoltage protection circuit as described in claim 1.

9. The switching power supply system according to claim 8, characterized in that, The switching power supply system is a flyback switching power supply system.

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